Underwater robots have achieved tremendous practical applications in underwater environment detection, monitoring, underwater target capture and underwater facility operations and the like. A manual method for overhauling a deepwater dam is very difficult. The overhaul via an underwater robot has become a main choice. Accurate positioning of the underwater robot is the key to the underwater overhaul of a dam with irregular dam surfaces, of a deepwater reservoir. An existing underwater robot positioning system cannot be directly applied to the overhaul of the irregular dam surfaces of the reservoir, as the reservoir dam is constructed in a deep valley area where the water level is high and the water is turbid, and the requirement for the positioning accuracy of the underwater robot is very high, the influence of sound wave reflection on a conventional sonar system for use underwater such as in seas and the like is very small, while sound wave reflection sources of the irregular dam surfaces of a reservoir in a deep valley area are numerous, for example, dam types, hoists, gates, sound of water flow, noise, embedded parts of dam surfaces and other buildings generate greater influence on the sound waves, and thus different quadrant reflection devices must be used to reduce the reflection and the multipath effect.